Methods and devices configured for dissolving hyperpolarised solid material with a solvent within a cryostat for NMR analyses

ABSTRACT

The present invention relates to devices and method for dissolving solid polarised material while retaining a high level of polarisation. In an embodiment of the present invention a material is polarised in a strong magnetic field in a cryostat  2  and then brought into solution while still inside the cryostat  2.

This application is a filing under 35 U.S.C. § 371 and claims priorityto international application number PCT/EP01/12736 filed Nov. 2, 2001which claims priority to U.S. Provisional application No. 60/256,974filed Jan. 5, 2001 and to Swedish application 0004034-5 filed Nov. 3,2000.

FIELD OF THE INVENTION

The present invention relates to devices and methods for dissolvingsolid polarised materials while retaining a high level of polarisation.

PRIOR ART

The present invention relates to nuclear magnetic resonance (NMR)analysis, particularly to nuclear magnetic resonance imaging (MRI) andanalytical high-resolution NMR spectroscopy. MRI is a diagnostictechnique that has become particularly attractive to physicians as it isnon-invasive and does not involve exposing the patient under study topotentially harmful radiation such as X-rays. Analytical high resolutionNMR spectroscopy is routinely used in the determination of molecularstructure.

MRI and NMR spectroscopy lack sensitivity due to the normally very lowpolarisation of the nuclear spins of the materials used. A number oftechniques exist to improve the polarisation of nuclear spins in thesolid phase. These techniques are known as hyperpolarisation techniquesand lead to an increase in sensitivity. However, in order to exploit theNMR signal for in vivo medical imaging the polarised material has to bebrought into solution or liquid phase before being introduced into theimaging object. For in vitro analytical NMR spectroscopy, it can alsooften be advantageous to bring the polarised solid material intosolution. A problem exists in that the polarised solid material has tobe brought into solution or liquid phase and transferred into the NMRmagnet with a minimal loss of polarisation. Patent application no.WO9935508 mentions a method for dissolving solid polarised material. Inthis method the polarised material was manually lifted out of thecryostat and within about 1 second dissolved in deuterium oxide at 40°C. while being subjected to a magnetic field of 0.4 T. This methodenhanced the polarisation by a factor of up to 21 compared to othermethods of producing a solution containing polarised material. Howeverthis method has the disadvantage that as the sample is moved manually itis difficult to get reproducible results. The purpose of the presentinvention is to provide methods and devices for improving the prior artmethod for producing a solution containing polarised material.

SUMMARY OF THE INVENTION

According to the present invention, at least some of the problems withthe prior art are solved by means of a device having the featurespresent in the characterising part of independent claim 1 or 12, andmethods having the features mentioned in the characterising part ofclaim 11 or 15. In particular the present invention provides a methodand means for bringing polarised solid material from a polarising unitinto solution or liquid phase with a minimal loss of polarisation.Devices and methods for producing solutions of dissolved hyperpolarisedmaterials, e.g. contrast agents or analytical samples, are described.

Further improved devices and methods have the features mentioned in thedependent claims.

In one embodiment of the present invention a sample is polarised in afirst instrument and dissolved in a second dissolving instrumentconnected to the first instrument. In a preferred embodiment of theinvention, a polarising device and a dissolving device are combined in asingle instrument, so that the transport time between being polarisedand dissolved is minimised and the loss of polarisation of the sample isminimised. In an especially preferred embodiment of the invention thepolarising unit and the dissolving chamber is combined with a NMRspectrometer and/or NMR imager so that the time between the sample beingdissolved and analysed is minimised and the loss of polarisation of thesample is minimised. According to the present invention, polarisationmay be achieved by use of a polarising agent, e.g. a compound comprisingparamagnetic organic free radicals. The NMR data obtained by the use ofdevices and methods in accordance with the present invention may be NMRimaging data and/or NMR spectroscopy data.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic lateral view of a first embodiment of a devicein accordance with the present invention;

FIG. 2 shows a schematic lateral view of a second embodiment of a devicein accordance with the present invention;

FIG. 3 shows a schematic lateral view of a third embodiment of a devicein accordance with the present invention; and,

FIG. 4 shows schematically a section through a device for injecting hotsolvent in accordance with the present invention;

FIG. 5 shows an embodiment of a sample-retaining container in accordancewith the present invention;

FIG. 6 shows schematically a lateral view of a device, for producinghypexpolarised materials by DNP, interfaced to a NMR spectrometer; and,

FIG. 7 shows schematically an embodiment of a magnetic resonancemeasurement circuit.

DETAILED DESCRIPTION OF EMBODIMENTS ILLUSTRATING THE INVENTION

In methods and devices in accordance with the present invention, a solidsample of the material to be polarised can be polarised while still inthe solid phase by any appropriate known method, e.g. brute forcepolarisation, dynamic nuclear polarisation or the spin refrigeratormethod, while being maintained at a low temperature (e.g. under 100 K)in a strong magnetic field (e.g. 1-25 T). After the solid material hasbeen polarised, it is brought into solution with a minimum loss ofpolarisation. In the following the expression “unit for dissolvedpolarised material” will be considered to mean the following: acontainer in which solid polarised material can be brought into contactwith an amount of solvent sufficient to dissolve the solid polarisedmaterial, and/or, a container in which dissolved polarised material canbe stored. The expression “dissolved” means that the molecules of asubstance said to be dissolved in a solvent are homogeneouslydistributed in said solvent.

In a first embodiment of the present invention, the dissolving occurs ina unit for dissolved polarised material that is physically separatedfrom the polarisation device, and the unit for dissolved polarisedmaterial is also physically separated from the analysis device andtherefore the polarised material needs to be transported from one deviceto another. In general, this has to be done rapidly, reproducibly andunder special conditions, as will be described in detail below for anumber of different examples.

In a second embodiment of the present invention the dissolving takesplace in the same apparatus that contains the polarisation device.

In a third embodiment of the present invention the solution of polarisedmaterial is made and used while retained in a combined polarisation,dissolving and NMR analysis device.

In a fourth embodiment of the present invention, material is polarisedin a polarising apparatus in close proximity to a NMR spectrometer, thepolarised material is dissolved in the polarising apparatus and thenquickly transferred to the analysis region of the NMR spectrometer.

The advantage of the described invention is that it provides means forbringing polarised solid material into solution with minimal loss ofpolarisation in a repeatable manner. This is crucial to the use of thesolid state hyperpolarisation techniques in medical imaging andanalytical in vitro high-resolution NMR spectroscopy. In solution, theNMR lines are narrow. This improves considerably the signal-to-noiseratio and spectral resolution, and also gives technical advantages sincethe sample does not have to be spun as for solid samples.

For most solid materials the relaxation rate (loss of polarisation ifhyperpolarised) increases rapidly as a function of inverse fieldstrength. Therefore, for these polarised materials it is preferable thatthey are kept in a strong magnetic field (e.g. greater than 0.1 T) whilebeing handled. Other reasons for the loss of polarisation are alsoknown, e.g. sudden changes of magnetic field orientation, strongmagnetic gradients, or radio frequency fields, and these should beavoided as much as possible. The dissolving of the polarised materialcan be promoted by several methods. When possible, the solid materialshould be provided as a finely divided powder in order to allow fastdispersion and intimate contact of the solid particles and the solvent.The solid particles (or beads) and solvent can be vigorously agitated bystirring, mixing, shaking, bubbling, crushing, sonication, microwaveheating, laser irradiation or any other means that will provideagitation, and optionally, heating. The temperature of the solvent canbe optimised for the particular material in order to provide the fastestpossible dissolving without causing unnecessary relaxation. Therelaxation rate as a function of temperature and field is unique toevery solid material and solvent/solute system. It is therefore alsoadvantageous when the temperature of the solvent is optimised forminimal relaxation of the actual material being dissolved. In general,but not always, the magnetic field should be as strong as possible. Thisalso applies to the liquid sample during the process of dissolving. Theminimum T₁ during the process will generally increase with increasingmagnetic field.

In a preferred embodiment of the present invention, a device fordissolving a solid polarised material is provided in a dynamic nuclearpolarisation (DNP) system. This DNP system comprises a magnet with fieldstrength of 0.1-25 T or more that is placed in a low loss cryostat inorder to achieve optimal cryogenic hold times. For magnetic fields aboveca. 2 T the magnet may be superconducting. For lower fields simplermagnets could be preferred. An especially preferred DNP system consistsof a superconducting magnet designed for a field-strength of 2-25 T. Themagnet is placed in an ultra low loss cryostat to achieve optimalcryogenic hold time. The field homogeneity required is sample dependent,but will typically have to be +/−0.2 mT over the sample volume. This canbe achieved by providing field shims even for large samples.Correspondingly, the stability of the field during polarisation shouldbe better than the homogeneity criterion, i.e. the field drift should beless than the inhomogeneity. The magnet is designed to accommodate a lowtemperature space to cool the sample. The preferred superconductingmagnet cryostat is preferably provided with a pumped helium bath or atleast a cold space in the bore of the magnet. The helium bath may becontained in a tube that is thermally insulated (e.g. vacuum insulated)from the magnet helium reservoir but connected to it by a capillary toallow filling from the magnet reservoir. The low temperature space maysimply be a cylinder (made from thin-walled stainless steel or copper oranother non-magnetic material or combinations thereof) with the lowerend closed. In order to obtain the lowest possible temperatures andlowest cryogenic consumption, the low temperature space is preferablyplaced in vacuum inside the helium can of the superconducting magnet andthe low temperature cylinder can preferably be thermally anchored atappropriate places in the bore, for example to the helium vapour-cooledshield and the liquid nitrogen-cooled shield or the like. The lowtemperature cylinder can preferably be connected to the helium canthrough a capillary at its base. The flow of helium may be controlled bya needle valve regulated from exterior, manually or automatically bycomputer control means or the like. The flow of helium into the heliumbath may be controlled by a motorised needle valve. The level of theliquid can be monitored, e.g. by an Allen Bradley carbon resistor meter,and the needle valve controlled manually or automatically to maintain afixed level. In order to achieve lower temperatures of the order of 1 K(⁴He), the bath can be pumped and the temperature of the bath can beascertained through the helium vapour pressure measured, for example, byan absolute capacitance transducer or Pirani element. If cooled by gasthen a temperature measurement can be used to control the needle valve.The cryogen, e.g. helium or nitrogen, could also be supplied from anexternal reservoir. Closed cycle refrigerators (‘cryogen free’) couldalso be envisaged, both for magnet cooling and cooling of the coldspace. The sample is polarised by microwave irradiation at the properfrequency. A microwave arrangement is provided for irradiation. Themicrowave arrangement can be implemented in a number of ways. For lowerfrequencies (less than ca. 200 GHz) a wave-guide may be used to guidethe waves to the sample space. At higher frequencies quasi-opticalmethods can be employed. The sample space is preferably constructed as aresonant microwave structure. The microwave structure is preferablyconfigured to allow easy placement and exchange of samples and anefficient cooling of samples. Once polarised the sample is dissolved bymeans of a device and method in accordance with the present invention asdescribed below.

An example of a first embodiment is shown in FIG. 1. The figure shows acryostat device 1 for polarising a solid material which device 1 isprovided with solid polarised material dissolving means in accordancewith a first embodiment of the present invention. Device 1 (shownenclosed by dashed lines) comprises a cryostat 2, containing apolarising means 3, e.g. a microwave chamber 3 a connected by a waveguide 3 b to a microwave source 3 c, in a central bore 6 surrounded bymagnetic field producing means such as superconducting magnet 5.Cryostats and polarising means for polarising solid material are wellknown from the prior art and their constructions will not be describedin detail. The bore 6 extends vertically down to at least the level of aregion P near the superconducting magnet 5 where the magnetic fieldstrength is sufficiently high, e.g. between 1-25 T, for polarisation ofthe material to take place. The central bore 6 is sealable and can beevacuated to low pressures e.g. pressures of the order of 1 mbar orless. A sample-introducing means such as a removable sample-transportingtube 7 can be contained inside the bore 6 and this tube 7 can beinserted from the top of the bore down to a position inside themicrowave chamber 3 a in region P. Region P is cooled by liquid heliumto a temperature low enough for polarisation to take place, e.g.temperatures of the order of 0.1-100 K. Tube 7 can be sealed at itsupper end in any suitable way in order to retain the partial vacuum inthe bore 6. A sample-retaining container, such as a sample-retaining cup9, can be removably fitted inside the lower end of sample-transportingtube 7. This cup 9 is intended to hold any material introduced into tube7. Cup 9 is preferably made of a light-weight material with a lowspecific heat capacity such as a foamed plastic, e.g. polystyrene, sothat the heat capacity of the cup 9 is as low as possible. A sealable Heinlet tube 10 (shown by a dashed line for ease of illustration) extendsfrom the top of bore 6 to the base of cup 9.

The device 1 further comprises means for extracting material from thesample-retaining cup 9. These means for extracting material can comprisean extraction tube 11 that extends from a short distance above the baseof sample-retaining cup 9, via a valve 14 to a unit for dissolvedpolarised material 15. Valve 14 can manually, or preferably, undercomputer control, be opened to allow communication between extractiontube 11 and the unit for dissolved polarised material 15, and can beclosed to prevent such communication. Unit for dissolved polarisedmaterial 15 has a hollow body 16 and can be provided with means to speedup the dissolving of solids such as mixing, stirring or agitating means17 such as an electric knife mixer with blades 19. Preferably allsurfaces that polarised material may come into contact with are coatedto prevent polarised molecules coming into contact with paramagneticirons. Unit for dissolved polarised material 15 is preferably surroundedby means for producing a storage magnetic field, such as a permanentmagnet 20 or an electromagnet. The expression “storage magnetic field”is intended to mean that the field strength inside the unit fordissolved material 15 should be sufficient to maintain the materialhyperpolarised for a period of at least a few seconds and preferably forsome minutes. The unit for dissolved polarised material 15 can be atleast partly filled with a solvent 21 suitable for dissolving of thematerial. A source of vacuum V is connectable to the unit for dissolvedpolarised material 15 via a valve 23 which is preferablycomputer-controlled by a computer 28. The base of unit for dissolvedmaterial contains an outlet 25 that is provided with a valve 27,preferably computer-controlled, for controlling the discharge of thecontents of unit for dissolved polarised material 15. The use ofcomputer-controlled, or otherwise automate valves, is preferred as thispermits the timing of the opening and closing of the valves to becontrolled in an accurate and reproducible manner. Naturally, anoperator may be used to initiate a process, for example, by pressing astart button or issuing a start command to a computer.

An example of a method using the first embodiment of the presentinvention for producing a solution of a dissolved material that has beenpolarised while in the solid state has the following steps:

-   the solid material in the form of powder, grains or beads is    introduced into the sample-retaining cup 9 at the bottom of the    sample-transporting tube 7;-   sample-transporting tube 7 is introduced into bore 6 so that    sample-retaining cup 9 is positioned in a magnetic field of the    necessary field strength, bore 6 is made vacuum tight and evacuated    to its working pressure;-   the still solid material is hyperpolarised;-   unit for dissolved polarised material 15 is partly filled with    solvent;-   bore 6 is repressurised to atmospheric pressure, where after the    upper end of He inlet tube 10 is unsealed;-   if the sample-retaining cup 9 is under the surface of the liquid    helium in the cryostat then the sample-retaining tube 7 is raised    until it is above the surface of the helium;-   valve 27 of the outlet 25 is closed and the valve 23 leading to the    vacuum supply is opened so that an underpressure occurs in body 16.    Valve 23 is closed, valve 14 is opened and the underpressure    reigning in body 16 leads to suction forming at the end of    extraction tube 11 in the sample-retaining cup 9 and a flow of He    from the upper end of He inlet tube 10 through extraction tube 11 to    the unit for dissolved material 15. With a suitably high suction,    this flow of He gas sucks the hyperpolarised material through tube    11 into the body 16 of the unit for dissolved polarised material 15;-   the mixing, stirring and agitating means 17 is actuated while the    solid material is sucked into the solvent in order to speed up the    dissolving process;-   after the material has entered the body 16, valve 23 is closed;-   after the material has dissolved the solution of the polarised    material can be dispensed through outlet 25 by opening valve 27.

The above embodiment of the invention can be adapted by providing othermeans for removing the solid hyperpolarised material from the polarisingunit. The solid material can for example be ejected from the polarisingunit by means of a pulse of pressurised gas (e.g. helium if the sampleis in a helium bath). The gas could be introduced into the He inlet tubevia a tube from a flask of compressed gas. Or it could conceivably begenerated from the bath of liquid helium by supplying a predefinedamount of heat to the bath, e.g. by resistive heating, therebyvaporising some of the helium. Or the solid material could betransported from the polarising unit to the unit for dissolved polarisedmaterial by mechanical means. For example, instead of extraction tube11, the sample-transporting tube 7 can contain a movablesample-retaining container, or shuttle, for containing the polarisedmaterial. This movable container can be raised or lowered, for exampleby being connected to a cable or rod, which is connected to an actuatingmeans such as a motor or weight or spring or the like, from thepolarising unit to the unit for dissolved polarised material and backagain. Once it is in the unit for dissolved polarised material themovable container can tip over, or in some other way deposit the solidmaterial into the solvent. The material container could also be moved bya spring, which is tensioned as the material container is lowered intothe polarising unit. When it is desired to extract the container fromthe polarising unit, the tension in the spring is used to rapidly dragthe containing from the polarising unit; or, a loop of high temperaturesuperconductor may be included in the sample holder and a current can beinduced in this loop by a surrounding coil. The current can be inducedin such a direction that it sets up a magnetic field opposing the mainmagnetic field, thereby ejecting the sample holder from the samplereceiving tube.

In order to limit the loss of polarisation of the dissolved material,the transportation means should be arranged so that the transit time ofthe polarised material is less than the T₁ (spin-lattice) relaxationtime of the material while it is being transported from inside the highmagnetic field in the cryostat to inside the magnetic field of the unitfor dissolved material or other container or apparatus. Preferably thistransfer period should be so short that it leads to less than 99% lossof polarisation, more preferably less than 90%, even more preferablyless than 10%. The transfer time can be reduced by decreasing thepressure in the unit for dissolved polarised material or adjusting thespeed of the mechanical transportation means, etc. During thetransferring of the polarised material from the polarising unit, themagnetic field surrounding it will decrease as it moves away from thesuperconducting magnetic. The polarisation of some materials relaxes inlow magnetic fields after only a few seconds or much less. In thesecases, a strong local magnetic field may be provided by a permanentmagnet, superconducting or resistive loop close to the material at leasttemporarily during the transport. Additionally the transport distancesand transfer times should preferably be made as short as possible. Inorder to achieve the best results, the polarising unit and the unit fordissolved polarised material should preferably be placed in a strongmagnetic field, e.g. of the order of 0.1-25 T. As is obvious to theskilled person the actual magnetic field strength required in any casewill vary with the type of solid and dissolving method used. For somemolecules the relaxation in solution is temperature dependent and anoptimal temperature of the solution can be chosen to preserve thepolarisation for as long as possible. In general, but not always, themagnetic field should be as strong as possible during the dissolving.The minimum T₁ during the process of dissolving will generally increasewith increasing magnetic field. Furthermore, the relaxation time willdepend on the magnetic field and an appropriate magnetic field can beapplied during transport of the solution (for example during transportof the solution from the polarising means to the imaging magnet).

In order to keep the solid hyperpolarised material as cold as possibleduring its transportation to the unit for dissolved polarised material,it is preferable to use materials which have a low thermal conductivityand low specific heat capacity for the tubes, e.g. Teflon™,polyurethane, silicon or the like. Additionally the tubes could be madedouble walled and/or silvered in order to reduce heat transfer byconduction and/or radiation.

In a second embodiment of the present invention, illustratedschematically in FIG. 2, dissolving of the hyperpolarised material inthe sample-retaining cup 9 can be performed while the material is stillinside the cryostat device 1. This can be achieved by providing asolvent introducing means. This can, for example, be achieved bysupplying a suitable high-pressure gas or fluid HP, e.g. air or heliumor solvent, to valve 23 as shown by dotted lines in FIG. 2.

An example of a method using the second embodiment of the presentinvention for producing a solution of a solid material that has beenpolarised while in the solid state has the following steps:

-   the solid material in the form of powder, grains or beads is    introduced into the sample-retaining cup 9 at bottom of the    sample-transporting tube 7;-   sample-transporting tube 7 is introduced into bore 6 so that    sample-retaining cup 9 is positioned in a magnetic field of the    necessary field strength, bore 6 is made vacuum tight and evacuated    to its working pressure;-   the still solid material is hyperpolarised;-   unit for dissolved material 15 is partly filled with solvent;-   bore 6 is repressurised to atmospheric pressure and the upper end of    He inlet tube 10 is unsealed;-   if the sample-retaining cup 9 is under the surface of the liquid    helium in the cryostat then the sample-transporting tube 7 is raised    until it is above the surface of the helium;-   valve 27 of the outlet 25 is closed and the valve 23 is adjusted so    that it connects the body 16 to the high pressure gas or liquid    supply HP so that an overpressure occurs in body 16. Valve 14 is    opened. This leads to solvent from body 16 being forced into the    sample-transporting tube 7. Once a volume of solvent sufficient or    more than sufficient to dissolve the solid material has been    delivered to the sample-transporting tube 7, valve 23 is closed. The    solvent in the sample-transporting tube 7 comes into contact with    and dissolves the hyperpolarised solid material in the    sample-retaining cup. Optional mixing, stirring or agitating means    (not shown) acting on the material in the sample-retaining cup 9 can    be provided in order to speed up the dissolving of the material.

If it is desired to then extract the solution of dissolvedhyperpolarised material from the cryostat (instead of analysing it insitu) then the valve 23 leading to the vacuum supply is opened so thatan underpressure occurs in body 16. This leads to suction forming at theend of tube 11 in the sample-transporting tube 7 and a flow of He fromthe He inlet tube 10 through tube 11 to the unit for dissolved material15. This flow of He sucks the solution of hyperpolarised materialthrough tube 11 into the body 16 of the unit for dissolved polarisedmaterial 15;

-   after the material and solvent have entered body 16, valve 23 is    closed;-   a mixing, stirring and agitating means 17 in the unit for dissolved    material is optional in this embodiment, but if it is provided then    it can be actuated for a predetermined period of time in order to    ensure that the solid material is fully dissolved;-   the solution of the hyperpolarised material can then be dispensed    through outlet 25 by opening valve 27.

Preferably this method is automated, for example by being controlled bycomputer (not shown), and computer-controlled actuators (not shown) areprovided to operate valves and mixing, stirring or agitating means.

In a further embodiment of the present invention a solvent can be addedto the sample-retaining cup 9 by simply injecting the solvent into theopen upper end of sample-transporting tube 7. The solution of solventand dissolved polarised material can then be aspirated in any suitablemanner, or the solution can be ejected through an outlet by injectingmore solvent or a gas or the like.

When the polarised solid material is brought into solution phase insidethe polarising unit by introducing the solvent into the polarising unitas in the second embodiment of the present invention, the polarisedsolid material is dissolved while kept in the strong magnetic field ofthe polarising unit or close to the strong magnetic field area of themagnet. If the material is polarised in a helium (or nitrogen) bath, thematerial can be raised from the bath to drain the liquid coolant priorto dissolving. The sample would still experience a significant part ofthe magnetic field of the polarising unit. The solvent can then beintroduced into the sample retaining cup and mixed with the solidmaterial to rapidly dissolve the solid after which the solution could beextracted with a syringe (either manually or automatically) or by a flowsystem as described above and injected into the item being imaged orsimply directly analysed by solution NMR.

Several factors have to be taken into account when the polarised solidmaterial is brought into solution phase inside the polarising unit. Asmentioned above, one factor is heat loss of the liquid entering thepolarisation unit, as it is important that it does not freeze when itcomes into contact with the cold sample-retaining container and solidmaterial. Therefore the amount of solvent added should have a mass andspecific heat capacity such that it has enough thermal energy to preventit from freezing when it is dissolving the solid material. Water is agood choice of solvent due to its high specific heat capacity and highlatent energy of solidification. It is also the solvent of choice forbiological reasons when the sample is to be used in vivo. Other suitablesolvents are biological buffers such as Ringer's acetate. When thesample is to be analysed by NMR spectroscopy or analytical highresolution NMR spectroscopy, a wider range of solvents is possible andit is especially advantageous to use water with anti-freeze additivessuch as glycerol. Another important factor is the design of the tubingto introduce the solvent and the design of the sample-retainingcontainer. Lightweight materials with poor thermal conductivity and alow specific heat capacity are preferred so that the heat energy lost bythe solvent to the tubing when descending into the bore and the energylost to the sample-retaining container are kept to a minimum. Typicalsuitable materials are Teflon™, polyurethane, PEEK, Aerogel™ andPerlite™. It can also be useful to use double wall tubing (the innertube might be inserted immediately prior to solvent addition). It canadditionally be advantageous to evacuate the space between the walls ofdouble wall tubes. Tubes can also be silvered or coated with aninsulating film (for example aluminised Mylar™). It can also beadvantageous to include a wrapping of resistive heating wire or film onthe tubing to improve the means of controlling the temperature of thesample. Another factor to take into account is the material used formanufacturing the sample-transporting tube and any sample holder used.The same criteria for choice of material as above applies here butceramic materials can be especially suitable here. For example, it canbe useful to use a ceramic or foamy plastic material that is porous tothe extent that superfluid helium easily can circulate through the wallsof the sample receiving tube and/or sample holder to cool the solidmaterial while liquid water or other solvents cannot circulate throughthe walls. This allows the material to be cooled by immersing thesample-retaining container in the form of a cup or closed end tube in aliquid helium bath, then lifting the container above the surface of theliquid helium so that liquid helium drains out through the pores of thecontainer before adding the water. Subsequent to the dissolving of thesample, the sample has, in the case of in vivo applications, to beextracted from the sample holder. This can be done either by the methodsin accordance with the present invention described above e.g. by a flowsystem, where liquid is pumped through the sample holder, by suction orby pressurising the sample container and collecting the polarisedsolution outside the polarising unit in a unit for dissolved polarisedmaterial, for example in a syringe so that it is ready for injection into the subject.

In a third embodiment it is also conceivable to provide the analyticalNMR instrument in the same instrument as the polarising unit anddissolving unit. This is shown in FIG. 3, where there is a plurality ofanalysis coils 3 l-3 l″, i.e. nuclear magnetic resonance imaging coilsand/or nuclear magnetic resonance spectroscopy coils. Coils which can beused for field shimming and NMR signal acquisition can be placed inpositions that are known from high resolution analytical NMR. In thiscase, the unit for dissolved polarised material is the same as thesample-retainer cup, and the transport time is zero seconds. This isadvantageous, as in this case there is no need to move the sample out ofthe magnetic field of the superconducting magnet when performing theanalysis i.e. imaging or spectroscopy. Additionally, the low operatingtemperature of the coils immersed in liquid helium improves their signalto noise ratio by a significant factor (of more than 3). Therequirements concerning field strength may not be identical for thepolarisation and the NMR detection, and means may be provided for movinga sample from one part of the magnet to another. The NMR detection couldadvantageously be done at a lower or higher field than optimal for theDNP process. One implementation would therefore be that the DNPpolarisation is done in cold helium gas at the lower edge of the magnet(i.e. in a lower field, e.g. 3.35 T). The field would then have to beshimmed in this area to the required homogeneity. After the polarisationthe sample could then be lifted to the magnet centre (that has a higherfield, e.g. 9.4 T, and homogeneity) for dissolving and NMR detection.Furthermore, the sample could be lifted to an intermediate place fordissolving and then moved to the magnet centre for NMR detection.

A conceivable variation of the invention is the incorporation of amultiple sample holder into the device so that several samples can bepolarised at once or sequentially and either ejected or dissolved one byone. It is also conceivable to use a system where several samples aredissolved and analysed simultaneously. As is obvious to the skilledperson, a multiple sample holder system can be fashioned in manydifferent ways e.g. using a carousel type holder or a grid-type holder.

In a fourth embodiment it is possible to provide prior art NMR equipmentwith a device in accordance with the present invention in order toproduce an apparatus that can produce materials with a high polarisationby DNP. In order to do this the NMR equipment needs be provided with alow temperature space that is in a magnetic field. In order to achievethis, any ordinary NMR magnet that has a suitably wide bore size may beequipped with a flow cryostat and instrumentation as described below inorder to enabling the production of solutions of molecules with DNPenhanced nuclear polarisation. A flow cryostat is a vacuum insulatedchamber that may be inserted into the bore of a magnet normally designedto have a room temperature bore, thereby allowing the temperature of thebore to be lowered by a stream of a cold cryogen. The flow cryostat isusually connected to an external cryogen supply through a transfer lineand the flow of cryogen into the flow cryostat cools the bore of themagnet and forms a low temperature space. The flow cryostat may beequipped with means, described below, to enable the polarisation ofsolid materials by DNP and it may be equipped with instrumentation,described below, for the detection of nuclear signals in the solid stateand in solution. Note that in dedicated DNP systems for NMR analysis orproduction of hyperpolarised imaging agents the low temperature space ispreferably integrated into the magnet cryostat.

The embodiment described above discloses a DNP device, which performsthe present invention in an in situ approach (i.e. the polarisation,dissolving and NMR detection are both performed in the same instrument).It has the disadvantage that existing NMR spectrometers cannot easily bereconfigured for DNP enhanced spectroscopy. In order to overcome this, afurther embodiment of the present invention will now be described andillustrated in FIG. 6 in which a DNP device 71 comprising a magneticfield-generating unit 72, e.g. superconducting magnet, permanent magnetor electromagnet, provided with an internal cold space 73 where a samplecan be positioned and where a microwave-generating unit, for example,consisting of a microwave source 74 and a wave guide arrangement 75, canbe present in order to polarise the sample, is arranged in proximity toand connectable by a polarised material transfer line 76 to a NMRspectrometer 77. Further NMR coils 78 may optionally be present in theDNP unit in order to quantify the magnetisation of the sample in thesolid state and/or in solution). The polarised sample can be extractedfrom the cold space as a solid and dissolved in a unit for polarisedmaterial 79 (shown by dashed lines between the DNP unit 71 and the NMRspectrometer 77) or it can be dissolved in situ as described above. Someflexibility exists in the positioning of the DNP apparatus relative tothe NMR magnet. However as short a distance as possible is preferred inorder to reduce the transit time of the dissolved polarised materialbetween the DNP device and the NMR spectrometer. The advantage of thisconfiguration is that it can be provided as an upgrade for existing NMRspectrometers. The reconfiguration of the NMR spectrometer for DNPhyperpolarisation is quick and easy. Existing NMR probes (flow probes)can be easily interfaced and full advantage from current NMR technologycan be taken. The polarised liquid sample should leave the DNP apparatusas quickly as possible and be positioned in the flow probe active regionfor immediate NMR analysis and therefore accurate timing of the entirepolarisation, dissolving, transporting process and triggering of the NMRexcitation/acquisition once the sample is in the NMR spectrometer isrequired. This may conveniently be computer controlled in order toensure that the transit time for the liquid and the delay between itsarrival in the NMR spectrometer and the triggering of the NMRexcitation/acquisition is preferably shorter than the nuclear T₁.

FIG. 4 shows schematically a cross-section through an embodiment of asolvent heating and injecting device 41 suitable for injecting heatedsolvent into a sample-retaining container, e.g. a sample-retaining cupin a cryostat. Solvent heating and injecting device 41 comprises apressure container 43, capable of resisting pressures of at least 2 bar,and preferably 10 bar, which pressure container 43 can be heated byheating means such as heating coil 45 wrapped around pressure container43 and connectable via a switch or relay 46 to a power supply 47.Pressure container 43 is preferably thermally insulated, for example byan insulating jacket 49 that surrounds it. Pressure container 43 isprovided with an inlet 51, connectable via an inlet pipe 53 and inletvalve 55 to a supply of solvent 57, and an outlet 59 connectable via anoutlet pipe 61 and outlet valve 63 to a sample-retaining container (notshown). A pressure sensing device such as a pressure transducer 65 isconnectable to solvent heating and injecting device 41 in order tomeasure, and optionally display, the pressure in pressure container 43.The solvent heating and injecting device 41 works in the following way:

-   with outlet valve 63 closed, inlet valve 55 is opened to permit a    quantity of solvent sufficient to dissolve the polarised sample to    enter pressure container 43 and then valve 55 is closed;-   switch 46 is closed so that heating coil 45 is connected to power    supply 47 and the solvent in pressure container 43 is heated;-   the rise in temperature causes the solvent to begin boiling and this    causes the pressure inside the pressure container 43 to rise;-   when the pressure registered by pressure transducer 65 has reached a    predetermined value, e.g. 2 bar or 5 bar, which corresponds to the    temperature needed to dissolve the sample, power supply 47 is    disconnected, outlet valve 63 is opened and the excess pressure over    ambient pressure which is present in the pressure container 43    causes the solvent to be rapidly ejected via outlet pipe 61 to the    sample-retaining container where it dissolves the sample.

As shown by dashed lines, preferably valves 55 and 63, pressuretransducer 65 and heating coil 45 are connected to a control means suchas computer 67. Computer 67 is preferably provided with software forcontrolling solvent heating and injecting device 41 and, if applicable,for controlling means for removing the dissolved polarised sample fromthe sample-retaining container.

A sample holder and a suitable microwave structure may be placed in thecold space in order to achieve microwave irradiation of the sample. Themicrowave structure can be a horn antenna or a chamber attached to theend of a wave-guide (as shown in FIG. 5) or a set of Fabry-Perot mirrorsor any other suitable microwave irradiating structures. The microwavestructure is preferably designed to act as a resonance chamber formicrowaves in order to increase the strength of the microwave field inthe microwave structure. For the lower frequencies (less than ca. 200GHz) wave-guides may conveniently be used to guide the waves to theirradiating structure. The geometry and dimensions of the wave-guide arechosen in order to reduce microwave losses. Preferably the wave-guide isdesigned to have as low a heat load to the low temperature space aspossible, and can be made, for example, from silver plated thin-walledstainless steel. Corrugated wave-guides could also be used. At higherfrequencies quasi-optical methods can be employed, and the microwave canbe guided with lenses and mirrors. The microwave structure preferablyhas openings to allow an easy exchange of sample and efficient coolingof the sample. A suitable microwave oscillator generates the microwaves,e.g. an IMPATT diode oscillator, or an IMPATT amplified Gunn oscillator,or a BWO or the like. Furthermore, the microwave oscillator may be anintegrated part of the resonant structure for irradiating the sample.Thus the active device producing the microwaves may be physically placedin the magnet close to the sample whereby transmission losses would bereduced.

FIG. 5 shows a perspective view of part of an embodiment of a polarisingmeans 3 intended to be placed inside the cryostat of a DNP system. Thiscomprises a microwave chamber 3 a connected by a wave-guide 3 b to asource of microwave energy (not shown). Chamber 3 a has a substantiallycylindrical outer wall 3 d, an upper end plate 3 e and a lower end plate3 f.

Chamber 3 a is made of a microwave reflecting material such as brass.Upper end plate 3 e has a central circular opening 3 g with a diameteradapted to allow a sample-retaining cup 9 (not shown) to pass into thechamber 3 a. Upper and lower end plates 3 e, 3 f have a plurality ofcutouts 3 h which are covered by a microwave reflecting mesh 3 i whichallows liquid helium to enter the chamber 3 a while preventingmicrowaves from leaving the chamber 3 a through the cut-outs 3 h. Thechamber 3 a is mounted on the lower end 3 j of the wave-guide 3 b and aslot 3 k in the wall 3 d of the chamber 3 a is aligned with a similarslot 3 l in the lower end 3 j of the wave-guide 3 b in order to allowmicrowaves to pass from the wave guide 3 b into the chamber 3 a. Thedimensions of the slots 3 k, 3 l are adapted to optimise the flow ofmicrowaves into the chamber 3 a. For example, if the inner diameter ofthe chamber is 28 mm, the inner height is 28 mm and the internal widthof the wave-guide is 7 mm, then the slots can be 5-10 mm high and 2-7 mmwide. The lower end 3 j of the wave-guide 3 b is tapered towards thebottom in order to act as a microwave reflector for increasing theamount of microwave energy coupled into the chamber 3 a. Suitable anglesof taper depend on the dimensions of the wave-guide, the microwavefrequency used and the dimensions of the slots 3 l, 3 l, but can be fromabout 5° to 60°, but preferably from 15° to 30°. The dimensions of thechamber 3 a, wave-guide 3 b, slots 3 k, 3 l are adapted so that chamber3 a acts as a resonance chamber for the microwave energy. In order tomeasure the polarisation of a sample contained in a sample-retainingcup, the chamber can be optionally provided with a central NMR pick-upcoil 51. This can be suitably made of a cylinder 53 made of PTFEprovided with, depending on the static field orientation, helical orsaddle shaped copper windings (not shown) and connected to suitablesensing means.

In this embodiment, a sample is placed in a sample-retaining cup 9 andthe sample retaining container is lowered into the centre of the chamber3 a (inside the pickup coil if there is a pick up coil). The source ofmicrowave radiation is activated and the sample irradiated. It can thenbe dissolved by means of the methods described above (i.e. in situ inthe cryostat or in a unit for dissolve polarised material outside thecryostat) and the dissolved polarised sample held in the unit fordissolved polarised material, or some other container (e.g. the sampleretaining cup) in a strong magnetic field, until needed.

In a second embodiment of a chamber in accordance with the presentinvention, the lower end plate 3 f has a central hole 3 m of the samediameter as a sample-retaining cup 9. This allows the sample-retainingcup 9 to be lowered through the chamber 3 a and out the bottom of it. Asample-receiving container could be provided with a plurality ofvertically separated sample-retaining cups. These cups could each be theheight of the chamber 3 a or a fraction thereof. If they are the sameheight as the chamber 3 a then it would be possible to expose a firstsample in one cup to microwaves in the chamber 3 a while a second samplein a second cup is positioned outside the chamber, but still very closeto the strong magnetic field. When the first sample is sufficientlypolarised the sample receiving container can be moved vertically so thatthe second sample in the second cup is inside the chamber 3 a and thepolarised first sample in the first cup is maintained polarised in themagnetic field outside the chamber 3 a. This can be repeated until allthe samples have been polarised, then all the samples can be dissolvedat once, using one device, or a plurality of devices, for extractingmaterial from the sample-transporting tube. Alternatively, eachpolarised sample could be dissolved in turn and either stored in theliquid phase in its cup (which is therefore a unit for dissolvedpolarised material) in the strong magnetic field in the DNP unit or inanother unit for dissolved polarised material in the magnetic field ofan imaging or spectrometry device.

NMR detection is particular desirable for analytical applications. Forother applications NMR detection optionally provides a measure of thenuclear polarisation. The NMR detection coil could be of any knowndesign, e.g. solenoid or saddle shaped. Usually the coil (inductance) istuned to the NMR frequency with a capacitor and matched to thecharacteristic impedance of the cabling. The NMR coil could be tuned andmatched at a number of frequencies in order to detect the nuclei ofinterest. The capacitors could be mounted close to the coil in the coldspace. This would allow the highest Q-values to be obtained. In theevent that it is impractical to have the capacitors close to the coil,then they may be put outside the cold space and connected to the lowtemperature space via a transmission line. The transmission line couldbe coaxial, twisted pair, stripline, or any other suitable cabling. Thechoice will be a compromise between heat load to the cold space andsignal attenuation. Several coils could also be envisaged. They could betuned for two NMR frequencies and would allow double resonance NMR(decoupling, cross polarisation, etc) to be performed in both solidstate and liquid phase. This would also allow simultaneous detection ofnuclei of more than one nuclear species. The spectrometer would thenhave to have multiple receivers. Optionally, the NMR signal of thevarious nuclei could be acquired sequentially. In order to permitmultiple samples to be analysed in a short space of time, asample-carousal for moving samples may be provided. Additionally, thedissolving of the solid material may be detected by optical means, as inorder to perform reproducible NMR analysis it is important that thematerial to be examined is dissolved homogeneously. This may be checkedby using optional optical photo-detection means inside or outside theNMR analytical chamber. Since some of the nuclei of interest may havevery short T₁ values it can be important to secure analysis as soon asthe dissolving process is finished. It is therefore preferable to havemeans arranged for coincident excitation/detection of all nuclei ofinterest. If the NMR detection circuit is cooled then a bettersignal-to-noise ratio is obtained. Furthermore, cooling of the signalamplifier is often advantageous. Consequently the signal amplifier maybe positioned close to the NMR detection circuit and preferably in thecold space. Superconducting coils and SQUID detectors are other devicesthat are available to improve the signal-to-noise ratio.

A simple and cheap circuitry that can be used for simple polarisationmeasurements is shown in FIG. 7. The device is a simple radio frequencymagnetic resonance spectrometer. Such a device can be used to determinethe polarisation of the solid sample material before it is dissolved anduses any of the previous described detection coils. The RF circuitconsists of a VCO (voltage controlled oscillator) 81, a directionalcoupler 83, a 180-degree hybrid 85, a mixer 87, a LNA (low noiseamplifier) 89, a low pass filter 91, a PC data acquisition card 93, andtuned and matched MR (or excitation) coils 95 (giving magnetic field B₁)arranged to provide a nearly uniform field transverse to the directionof the static field B₀ from static field coils 97. The coils 95 aretuned to the MR frequency and matched to the characteristic impedance ofthe transmission line (e.g. 50 Ω). The VCO 81 (or function generator)generates a continuous wave signal that is split by directional coupler83 (divider) into two signals, which drives the local oscillator of themixer 87 and the other to 180-degree hybrid 85 feeding the MR coil 95.Fixed attenuators (not shown) may be used to adjust the signal levels.The VCO 81 should be capable of being frequency modulated over asufficient frequency range to cover the spectra range of interest. Themodulation rate could be typically 5-50 Hz, and the modulation signal issupplied synchronously with the signal acquisition (signal averaging).Preferably the modulation-signal and signal acquisition is generatedfrom a PC data acquisition card 93, and the signal is convenientlyavailable for further data analysis. A change of reflection coefficientis observed as the frequency is swept through the magnetic resonance.The reflection signal is amplified by the LNA 89 and fed to the mixer87. By adjusting cable lengths an absorption or dispersion signal can bechosen. The bandwidth of the MR coils 95 in itself produces a parabolicbaseline, which has to be subtracted from the signal. The baseline canbe acquired before introducing the sample or it can be fitted with apolynomial function (or a spline function) outside the signal regions.The coil bandwidth can be adjusted for optimal performance in a numberof ways, e.g. resistive damping, overcoupling which gives a betterresult, or, preferably, by actively loading the coils 95 with the LNA89. The natural bandwidth of a tuned coil in this frequency regime isseveral hundred Hz, providing insufficient bandwidth for mostapplications. Resistive damping increases the useful bandwidth to anacceptable degree. However, this compromises the signal-to-noise ratioby the square root of the increase. This is acceptable to some extentsince amplitude and phase-noise of the VCO often determine thesignal-to-noise ratio. The magnetic field could be anything from a fewmT to many T depending on the gyromagnetic ratio of the spin and thefrequency of the VCO 81.

As is clear to the skilled person, in a method in accordance with thepresent invention the presence of a strong magnetic field, and,optionally, elevated/optimised solvent temperature, agitation, and afinely divided solid sample minimises the polarisation loss duringdissolving. The amount of polarisation retained during the dissolving ofany particular solid polarised material depends on, amongst others, thefollowing factors: the composition of the polarised material, the formand size of the material (e.g. whether it is in the form of beads,powder, particles, or is present as a solid mass) the solvent used todissolve it, the solvent temperature, the speed of dissolving, themagnetic field the dissolving takes place in. By optimising thesefactors for each material, loss of polarisation can be made negligible.The optimum conditions for the dissolving a sample while retaining ahigh level of polaraisation can be readily found experimentally Thefollowing experimental results show the results of varying the timetaken to dissolve a sample, all other variables remaining the same:dissolving 1 mm diameter beads of HP001(1-hydroxymethyl-1-13C-cyclopropyl)-methanol, doped with 15 mM OX063, inD₂O at a temperature of 360K in a time of 3 s in a magnetic field of3.35 T resulted in a loss of polarisation of less than 10%. Dissolvingthe same substance in 8 s resulted in a loss of polarisation of 69%.Performing dissolving of the same substance in 12 s caused a loss ofpolarisation of 97%. These results were reproducible and allow thedegree of polarisation lost during dissolving at different rates to beestimated. Thus, these results show that dissolving HP001 in 12 secondsleads to a loss of polarisation of less than 99% (actually 97%),dissolving HP001 in 8 seconds leads to a loss of polarisation of lessthan 90% (actually only 69%) and dissolving HP001 in 3 s causes a lossof polarisation of less than 10%. More rapid dissolving, for exampleachieved by more agitation or a higher solvent temperature leads to evensmaller losses in polarisation between the solid and liquid states.

The above mentioned embodiments are intended to illustrate the presentinvention and are not intended to limit the scope of protection claimedby the following claims.

1. A device configured for polarising a solid material and dissolvingsuch a solid polarised material in a solvent wherein said devicecomprises a cryostat (2) configured to receive a sample-retainingcontainer and configured for retaining a sample of the solid materialand comprising magnetic field generating means (5) and means (3 a-3 c)for polarising the solid material, wherein said device further comprisesmeans for dissolving the solid polarised material (14, 15) in saidsolvent in said sample-retaining container (9) while saidsample-retaining container is inside said cryostat (2).
 2. A device inaccordance with claim 1, further comprising means for extracting andtransporting said polarised material, said means for extracting andtransporting said polarised material being configured to transport saidpolarised material in solution from said sample-retaining container (9)inside said cryostat to a unit for dissolved polarised material (15)arranged outside said cryostat.
 3. A device in accordance with claim 2,wherein said means for extracting and transporting said polarisedmaterial is further configured to transport solvent to saidsample-retaining container (9) positionable inside said cryostat.
 4. Adevice in accordance with claim 1, wherein the loss of polarisationduring dissolving of said polarised solid material is less than 99%. 5.A device in accordance with claim 1, wherein the loss of polarisationduring dissolving of said polarised solid material is less than 90%. 6.A device in accordance with claim 1, wherein the loss of polarisationduring dissolving of said polarised solid material is less than 10%. 7.A device in accordance with claim 2, wherein said unit for dissolvedpolarised material (15) is provided with agitating, stirring or mixingmeans (17, 19).
 8. A device in accordance with claim 1, wherein saiddevice further comprises a dynamic nuclear polarisation system.
 9. Adevice for nuclear magnetic resonance analysis comprising the device ofclaim 1 and nuclear magnetic resonance analysis coils (31-31 ″).
 10. Amethod for producing a solution containing a dissolved polarisedmaterial, said method comprising the steps of: introducing into acryostat (2) of a device according to claim 1 a solid material in asample-retaining container (9); polarising said solid material insidesaid cryostat (2) of said device; and dissolving said polarised materialin said sample-retaining container (9) in a solvent while still insideof said cryostat (2) of said device.
 11. A method in accordance withclaim 10, wherein the loss of polarisation of said polarised solidmaterial during said dissolving step is less than 99%.
 12. A method inaccordance with claim 10, wherein the loss of polarisation of saidpolarised solid material during said dissolving step is less than 90%.13. A method in accordance with claim 10, wherein the loss ofpolarisation of said polarised solid material during said dissolvingstep is less than 10%.
 14. A device in accordance with claim 1 whereinthe sample-retaining container (9) is a multiple sample holder andseveral samples of the solid material can be polarised at once orsequentially.
 15. A method in accordance with claim 10 wherein thesample-retaining container (9) is a multiple sample holder and severalsamples of the solid material can be polarised at once or sequentiallyand wherein said several polarised samples are dissolved one by one orsimultaneously.
 16. A method in accordance with claim 10 whereinsubsequently NMR analysis of the dissolved polarised material isperformed.